A craft, once anchored, tends to move as a function of the stresses exerted thereon, and in particular by the wind. Such displacements are all the greater as, for a given tonnage, the surface exposed to the wind is large. Furthermore, the use of materials of the composite type, which are much lighter, reduces the tonnages for a given length of the craft and lateral surface thereof; such reduction in the tonnage correlatively reduces the inertia of the craft. Displacements when anchored bring about repeated variations in tension on the anchor chain or cable, which may cause the anchor to be torn away, which is the principal cause of wrecks. In order to simplify the following description, the term "chain" will alone be used, it being understood that another anchoring means such as a synthetic cable may also be employed.
U.S. Pat. No. 3,055,322 discloses so-called "sentinel" devices intended to improve the stability of the craft by performing to some extent a role of damper of the variations exerted on the chain. These devices consist in a heavy piece which is fixed on the cable between the anchor and the craft. Normally, the sentinel rests on the sea-bed; if the tension increases further to the craft drifting, the sentinel rises so that the subsequent increase in weight opposes the movement of the craft. The sentinel is solidly fixed to the cable with the aid of a retaining system which imprisons the cable.
This device, which has been known for about thirty years, is not entirely satisfactory, principally because assembly thereof requires that the anchor be raised and the zone of the chain where said device must be fixed be accessible to the operator. Furthermore, it is rigidly fixed to the chain and its position cannot be changed when the anchor is cast.